Polyurethanes are a well-known class of commercially available polymers. Polyurethane foams have great versatility and many formulations and manufacturing processes have been developed to take advantage of these properties. Most of the flexible foams, to which the invention relates, are made with toluene diisocyanate (TDI) and, while pure methylene diphenyl diisocyanate (MDI) has found applications in rigid foams, high resilience self-skinning molded flexible foams and cold-cured quick demolding foams for furniture cushions, other attempts at developing flexible foam using MDI, methylene-bridged polyphenylene polyisocyanate (PMDI), modified MDI and even TDI/MDI mixtures have not been as successful. See Woods, Flexible Polyurethane Foams Applied Science Publishers, 1982, pages viii, 16-25, 150, 153,315.
A blowing agent is necessary for making foams. The primary blowing agent in most foams is water and the foam density decreases with increased water, with amounts up to about 5 parts per hundred polyol. However, hardness also increases as the level of water increases. In furniture and auto cushions, however, it is sometimes desirable to have both a density decrease and a hardness decrease, without significantly lowering other properties of the foam, for reasons of cost and comfort. Presently, this is accomplished, in MDI- and TDI-based foams, through use of an auxiliary blowing agent, a chlorofluorocarbon, primarily F-11. Since the use of chlorofluorocarbons (CFC's) have been linked to depletion of ozone in the atmosphere, determined efforts are being made to reduce the use of CFC's. It is accordingly an object of the invention to produce a polyurethane foam of low density and hardness, comparable to CFC-obtained foams, without employing any CFC's in the formulations for making flexible foams.
Replacements for CFC's are being developed as the CFC's are phased out. For example, hydrochlorofluorocarbons (HCFC's) which can also be used as blowing agents for polyurethane foams and are not believed to be as damaging to the earth's atmosphere as CFC's, may be used until completely harmless blowing agents are discovered. The discovery of applicants can be used in conjunction with CFC's and/or HCFC's to produce a cumulative effect on the density of the foams produced to achieve ultimate densities lower than produced with only CFC's or HCFC's. Where the term "CFC" is used herein, HCFC's are also intended.
Secondary amines have previously been proposed as curing agents for TDI-based polyurethane foams, Gattuso et al Secondary Amine Extended Flexible Polyurethane-Urea Foams, Polyurethanes 88, Proceedings of the S.P.I. 31st Annual Technical/Marketing Conference, Oct. 19-21, 1988. However, with TDI-based foams (including those blended with substantial amounts of MDI-based isocyanates), the hardness (as measured by Indent Force Deflection (IFD) or Compression Force Deflection (CFD)) increases with increasing amounts of the secondary amines. The data thus indicates that these secondary amines would not be useful as a substitute for CFC in polyurethane flexible foams. It was entirely unexpected that the secondary diamines of the invention could be used to make MDI-based foams without any CFC's which would have low density and low hardness, comparable to those made with CFC's.
British Patent 1,412,818 discloses the use of asymmetrical aromatic diamines (mixed with varying amounts of coreactant symmetrical aromatic diamines) for making MDI- or TDI/MDI-based polyurethane foams. The disclosure does not relate to CFC-produced foams and, in fact, the MDI-based foams produced (Examples 8 and 15 of the patent) exhibited either the same or increased density as those produced without the diamines.
U.S. Pat. No. 3,846,351 describes the use of secondary phenylene diamines in combination with polyols as catalysts and chain extenders in the production of flexible polyurethane foams. More recently, it has been shown in U.S. Pat. No. 4,578,446 to House et al. that, contrary to the prior conventional wisdom, N-alkylated methylenedianilines are suitable curing agents for urethane prepolymers, i.e., in elastomer production via non-RIM processes. In U.S. Pat. No. 4,801,674, to Scott, et al., N-alkylated methylene dianilines are disclosed as suitable curing agents for RIM applications. However, neither patent discloses the unexpected and extremely beneficial results achieved with the present invention.